This invention relates to a method and apparatus for measurement of forces and moments using a displacement sensor.
The measurement of loads, both forces and moments, with accuracy and precision is important to many applications. A common use, where several moments and forces need to be measured, is in the testing of aerodynamic models in a wind tunnel. These devices, known as balances, typically come in two types. One of these is a strain-gauged device, which utilizes load cells or flexural elements. These are limited by the accuracy that the strain can be measured. Often the strain required to achieve adequate output causes fatigue in the flexural elements. Prior art for this type of balance includes U.S. Pat. No. 3,613,443, assigned to The Boeing Company. In contrast, the present instrument utilizes displacement sensors that are independent from the flexural elements. The second type is a null type balance. Typically these are made up of a very complex series of linkages that separate the forces and moments. The forces and moments are then reacted with a force generating device that returns the balance to a null position. These balances are nominally very complicated and generally more flexible than a strain gauge balance. The complexity often leads to designs that are expensive to design, fabricate, and maintain, and are also large in size. The flexibility of the balance results in movement of the balance calibration center, causing additional uncertainties to the data.
This invention represents a simplified configuration for a highly accurate multi-component force and moment transducer. Loads are applied causing the transducer to deflect. These deflections are measured with several displacement transducers. The measurements are then combined in an algorithm that resolves the displacements into forces and moments. The algorithm is based on geometry as well as on a calibration to establish relationships between the displacements and loads.